"no known bacteria that's harmful to man can survive in beer" was what I wrote, and that's true.
Infected beer contains no bacteria that's harmful to humans. It can contain plenty of other bacterias though,
Beer contains alcohol, alfa-acids, very little to no oxygen and co2. The bacteria that likes it there has no reason to like being inside humans.
"Enough alcohol", yes, but it wasn't easy brewing strong beer in those days. Especially considering the bad sanitation.

Please take into account that the beer made hundreds or thousands of years ago had very little alcohol.
Things like enzymes, temperature rests, fermentable extract, FAN and sanitation was unheard of.
Beer wasn't usually being drunk to get drunk. Beer was a more healthy alternative to water, since it contains a number of nutrients and energy, and also being harmless to drink since no known bacteria that's harmful to man can survive in beer.

No, it isn't.
Quality isn't at all about how good a beer tastes. That's completly subjective.
Quality is brewing a product that comes out just the way you wanted it to, and then brew it again, and again. It's about controll over all the parameters during milling, mashing, lautering, boiling, whirlpooling, cooling, aeration, fermentation, lagering, conditioning, filtration, storage, filling and alot of steps I missed.
If a customer thinks a beer doesn't taste good, that's not a sign of bad quality. If a customer drinks a beer that's been infected by bacteria or wild yeast, or damaged by oxygen or light, that's a sign of bad quality.

As a european brewer, who has worked for the two largest breweries in my country, two of the smallest and who currently works with planning and installing two new microbreweries, I don't agree.
If someone would ask me what's the most difficult beer to brew, I would say Budweiser (if I'm allowed to exclude lambics). Because making a beer that tastes virtually nothing isn't an easy thing to do. And to have every single bottle taste the same is even harder. American breweries have contributed ALOT to the quality aspect of the brewing industry. I don't drink beer with so little taste myself, but I appreciate the quality aspect of it.

For a homebrewer who brews one brew per week, no. There's not much reason. But for a brewery that boils 40-50 brews per week, they need to do it.
The wort kettle will accumulate alot of dirt over time. If you're using an internal heater, it will be covered by caramellized sugar that's pretty hard to remove without using strong cleaning agents. There will be little or no microbiological activity after a 60 minute boil, but the kettle will still be dirty from hop residue, proteins, calcium oxalate (beerstone) and fat.
I've been inside a mash kettle that hasn't been properly cleaned for years. Rust, layers of grease, biofilm, burned sugar. It was all stainelss steel, but you couldn't tell from looking at it.
The cleaning agents used also helps preserve the stainless steel that's used in most modern breweries.

Yeah, that's pretty much true!
Breweries uses CIP (Cleaning In Place), and that means pumping large amounts of cleaning agents (usually sodium hydroxide and some acid, phosphoric, nitric or other) for about two hours depending on what tank, tun, pipe, hose. And large amounts of water.
I have only worked at breweries. I'm a computer geek too, but I've never had the same passion for computers as I do brewing. Unless you're working in an office at a brewery, you're going to do alot of cleaning. At my previous job, I probably spent tree days a week swabbing floors, cleaning tanks, pipes and hoses.
A brewery is the only place I've found that has everything I'm interested in: chemistry, physics, automation and control systems, biochemistry, microbiology, biotechnology and brewing.
The brewing process is generally regarded as the oldest practice of biotechnology. You convert the starch, proteins, amino acids and alot more when you make malt out of grain. In the mash tun, you convert the remaining starches, proteins, beta-glucans etc to sugar and nutrition for the yeast. When you boil the wort, you coagulate proteins, isomerise (sorry, bad english. Not native language) the alpha acids in hops so they become soluable and more bitter. Mailard reactions gives the wort color and more flavour. Well, no need to ramble on. If someone would like some basic insight in the science behind the malting and brewing process, I recommend Beer: Tap Into The Art and Science of Brewing, buy Charles Bamforth. http://www.amazon.com/Beer-Tap-into-Science-Brewing/dp/0195305426/ref=sr_1_1?ie=UTF8&qid=1330353116&sr=8-1
Or this video with Charles Bamforth called Advanced Chemistry of Beer and Brewing: http://www.youtube.com/watch?v=M2Hk_FV8c-w
Oh, and I recommend anyone who are interested in beer and brewing to check out some homebrewing clubs that may be avalible in your area. Or check out http://www.homebrewtalk.com/
Homebrewing clubs is a good forum where you can learn and discuss brewing, hacking together improvements to the brew rig and brew beer with other people with the same interests.

As a homebrewer, sure, the sanitation may look like that.
But in an actual brewery, things are a bit different.
In the brewhouse: the malt mill, the mash tun, the lauter tun, the wort kettle, the whirlpool, the plate heat exchanger, all pipes and lines connecting them. The malt silos should also be cleaned, but not on a weekly basis or once a day.
The fermentation cellar: floor, hoses, pipes, fittings, propagation vessels, fermentation tanks, lager tanks, equipment for analysis. Several times a day.
The filter: floor, fittings, hoses, pipes, the filtration devices, pressure tanks. This needs to be done several times a day.
Filling hall: beer line from the filter, filling cylinders, the filling machines, rinsers, floors, transport bands... yeah, just about everything in the filling hall because at that point, the quality of the beer can not be improved, just maintained. Oh, and crates, bottles. Here everything needs to be sanitized several times a day.
At a modern brewery, there's ALOT of cleaning. At any given time, if you find yourself without anything to do you can always go and swab the floors with sodium hydroxide or chlorine.
In many cases in a brewery, sanitation needs to be done BEFORE and/or AFTER each process.
But yeah, different for most homebrewers.